1. Field of the Invention
This invention relates generally to liquid level indicators.
2. Prior Art
Gauges are commonly used for indicating fill levels in liquid holding tanks. U.S. Pat. No. 5,484,336 to McConnell; U.S. Pat. No. 2,696,738 to Lupfer; and U.S. Pat. No. 190,607 to McInnes each disclose a gauge comprising a fluid reservoir positioned at the bottom of a tank and immersed in a liquid in the tank. The reservoir is connected to a transparent vertical tube extending through the side wall of the tank near the bottom. A fluid in the reservoir is forced up the tube by the hydraulic pressure on the reservoir to indicate the level of the liquid in the tank. However, piercing the tank near its bottom and installing the tube through the aperture requires emptying the tank first. This cannot be done if the gauge has to be retrofitted to the tank because there is usually no place to hold the liquid temporarily outside the tank. The aperture through which the tube is positioned is also susceptible to leakage after installation. U.S. Pat. No. 813,096 to House discloses a gauge comprising a diaphragm at the bottom of a tank. A pipe is connected between the diaphragm and an indicator tube to transmit the air pressure in the diaphragm to a fluid reservoir at the bottom of the indicator tube. A fluid in the reservoir is forced up the tube to indicate the liquid level in the tank. However, air is compressible and thus cannot reliably transmit the pressure from the tank to the reservoir.
The objectives of the present liquid level gauge are:
to reliably indicate the level of a liquid in a tank;
to be installable without emptying the tank;
to avoid the possibility of causing leaks in the tank;
to be easily readable;
to remain readable after prolonged exposure to sunlight;
to prevent buildup of minerals and bacteria;
to be freeze resistant; and
to prevent itself from being obscured by any adjacent vegetation.
Further objectives of the present invention will become apparent from a consideration of the drawings and ensuing description.
The present liquid level gauge for a liquid holding tank is comprised of a first tube with an inner section positioned inside the tank, and an outer section positioned vertically outside the tank. A larger diameter transparent tube is positioned around the outer section of the first tube, and has a sealed lower end. The outer end of the first tube is open to the interior of the transparent tube. The inner end of the first tube is connected to a bladder positioned at the bottom of the tank. The bladder and the first tube are filled with an indicator fluid. The transparent tube is partially filled with the indicator fluid that flow from the outer end of the first tube. The height of the indicator fluid in the transparent tube is the same as the level of the liquid in the tank.